Treatment of clay by flotation



Patented July 15, 1941 Donald S. Phelps, Harvard, Masa, assignor to'Edgar Brothers Company, Metuchen, N. .L, a

corporation of New Jersey No Drawing. Application my 29, 1940, SerialNo. uazsa 6 Claims.

This invention relates to the treatment of clay by flotation. In recenttimes some effort has been made to eliminate impurities from crude claysby flotation treatments, and thus it has.

been proposed, for example, to separate impurities simply by oiling andfloating them; but such treatment appears to have been insumcientlysuc-, cessful' for any practical commercial use. Eflorts have also beenmade to treat clay by froth flotation, but so far as has beenascertained, such efforts have been unsatisfactory in attempting toseparate the impurities by elevating them in the froth, and'have been inany practical sense equally unsuccessful in attempting to carry up clayin the froth free of undesired particles.

For instance, oiling or like water-repelling agents clay,-of one of thevery impurities which are ordinarily undesired in important uses of claysuch as for paper coating. It is'accordingly an important object ofpresent invention to provide new and improved procedures and reagentsfor the treatment of clay to improve its quality, and biilticlllaiiy forthe refinement of clay by flotat on.

The invention is particularly directed to the treatment of clay by frothflotation for elevation in the froth, and consequent concentration, ofhydrated aluminum silicate, that is to say, actual clay material; sothat, for instance, the clay may thus be separated from contaminatingimpurities ordinarily found with it,ex'amples of such impurities beingmica, sand, ilmenite, tourmaline, particles of iron compounds, and clayparticles substantially, contaminated with compounds of iron ortitanium. To these ends, it has now been discovered that sulflte wasteliquor, viz., waste liquor from the manufacture of paper, pulp by thesulflte process, is a remarkably effective frothflotatlon agent forclay, and more specifically, that .it' has, in addition to frothingcharacterlstics a peculiar aptitude for carrying up clay in the frothwhile rejecting contaminating impurimarkably high recovery of pure clay,with simultaneous accumulation of the contaminating impurities in thetailings. That is to say, the sulflte waste liquor is found to have aspecific clayselecting power, and the strong tendency is,either for theimpurities to fail to get into the froth at all, or only to be carriedin the froth by entanglement rather than by selective action,-as

evidenced by the concentration of the impurities in the taillngs.

Although tests of the invention have been made with clays of variousstages of refinement. and in each case success has been obtained inimproving the quality of the clay, the invention ties such as mentionedhereinabove. This action of su lflte waste liquor, and its peculiar'aiflnity for kaolin in a froth, are evidencedby the fact that thebubbles of the froth are generally milky 60 with clay (and clay alone)throughout their areas, and by the results of numerous tests wherei inupon froth flotation treatment of a crude clay slip containing sulfitewaste liquor a froth conmay conveniently be illustrated by examplesrelating to the treatment of crude .clay as mined and as containingimpurities of the character described above. The crude clay, coming fromthe mine, is conveniently introduced in a blunger, for instance of theusual type employed to make crude clay slip, and a slip or pulp is thusobtained, containing, say from 3% to 35% of solids. Although the sulfitewaste liquor may be otherwise introduced, for example by incorpor'atingit in-the water prior to its mixture with the clay in the blunger, thematerial may be readily introduced in the prepared clay slip. Thoroughpermeation of the reagent in the slip having been obtained, the latteris fed to a suitable froth flotation apparatus for-produ'ction of afroth which is collected for recover of the improved clay.

Althoughother types of froth flotation cells may be employed, it appearspreferable to utilize direct aeration by blowing air or other gas intothe pulp. Thus, for example, good results have been had with the Callowtype of froth flotation cell, wherein the aeration is directly obtainedby blowing air through, and subdividing it with, a fine canvas screenbeneath the pulp column. Especially advantageous operation has beenachieved with a cell providing both direct aeration'and self-agitation,and comprising a series of ducts extending down into a. central pulpchamber for blowing air into the pulp, and ad- Jacent frothing chambersto which the agitated and aerated pulp passes and in which a risingfroth column, height, is produced to pass over into suitable collectinglaunders. It will be understood that in such cells the central chamberis preferably separated from the frothing chamber by depending baiiiesextending down into and slightly centrate has been obtained consistingof a rethe vigorousiniection f iriflle pulp is not only advantageouslyof substantial By way of specific example, an untreated white clay froma mine at'McIntyre, Wilkinson County, Georgia, was subjected to thefollowing procedure: The clay was blunged with water to produce a slipcontaining about 25% solids, and

after passing the slip through-sand-cone separators to remove coarsematerial such as coarse sand, gravel and the like, sulfite waste liquorwas incorporated'in the proportion of about 25 pounds per ton of dryclay. In this run the sulflte waste liquor was one obtained from a pulpmill in Maine, and was derived from sulfite treatment of a blend ofnorthern spruce and northern hemlock; it appearing from other tests thatsulflte liquor from these woods has preferable qualities for thepurposes of the present invention; The liquor had been somewhatevaporated, to have a specific gravity of about 1.28, i. e., so as toweigh about pounds per gallon.

After thorough mixing to obtain full permeation of the liquor in. thecrude clay suspension,- such permeation being apparently desirable toattain the optimum intimate action on the clay in the flotationtreatment,the resulting slip or pulp was fed to a flotation apparatuscomprising four cells of the combined agitation and aeration typedescribed hereinabove. The apparatus was conveniently so arranged as tofeed the froth concentrate from each cell (except the last) to the feedend of the next one in the series, and it was found desirable to breakdown the froth in each such transfer, for instance by running each frothto a corresponding storage tank and pumping the resulting refined pulpfrom the bottom of the tank to feed the next cell. The froth from cellNo. was collected, for recovery therefrom of a highly refined clay; andthe cells were connected in a closed circuit at the tails ends, so thatthe only tailings came from No. 1 cell.

That is, the tailings of the fourth cell were re-' turned into the feedof the third, those of the third into the feed of the second, and thoseof the second into the feed of the first, whereby the final concentrateconsisted of the collected froth of the fourth cell and the finaltailings were taken from the end of cell No. 1. Operation was had at therate of about one ton of original clay feed (dry weight of clay) perhour, and with an air pressure in the aeration ducts, of about one poundper square inch.

Upon operation of this system, clay bearing froth was collected asdescribed at each cell and the final froth concentrate (from cell No. 4)was found to provide a very satisfactory recovery or high qualitykaolin, and to be entirely free from any appreciable content of sand,mica, ilmenite or other contaminating particles, such as hard clayparticles and heavily iron-stained particles.

The solids content of the concentrate and the one 31-hour run of theprocedure of the example I described above; the impurities wereconveniently determined on the basis of the content, by weight,

of particles larger than about 25 microns, such particles substantiallyconstituting the impurities.

Solids Impurities Yield Percent Percent Percent 25 25 a; 2.0 n 92s Afurther run of about 20 hours under substantially the same conditionsresulted as follows:

Solids Impurities Yield Percent Percent 25 It will be understood thatmultiple flotation treatment is not necessary in all cases for efficientseparation of the clay from its contaminating particles; demands of theindustry vary and as a consequence the degree of purity required variesso that in some cases a single cell is ample to yield a product of thedesired quality.

As further examples of the invention, using other apparatus, thefollowing test runs were made: One thousand grams of untreated clay, ofthe character described above, were permitted to soak for two or threehours and introduced to a froth flotation cell of the Callow type, witha total of three kilograms of water. Seven cc. of

sulfite waste liquor were added in dilute solution as flotationprogressed; operation of the cell being initiated with the firstintroduction of the reagent and the resulting froth collected as aconcentrate. Flotation was very rapid, and the concentrate yielded arefined clay of good color, substantially free of impurities. The solidsin the concentrate, comprising purified kaolin, weighed 567.5 grams,whereas the solids in the tailing weighed 398 grams. As indicated, thesulflte waste liquor was employed in the proportion of about eighteenpounds per ton of clay.

In another run 1000 grams of the crude clay were similarly pulped andintroduced to the Callow cell with a total of three liters of water.12.5 cc. of the sulfite waste liquor was added, conveniently in a l to10 solution, and at the rate of about 3 cc. at a time over a period of/z hour during which the cell was operated. The froth was collected, andwhen broken down it appeared that the resulting concentrate containedabout 20% solids, constituting purified kaolin having a very good colorand free of contaminating particles, including not only the simplerimpurities but also the larger clay particles contaminated with iron orthe like. The solids in the concentrate weighed 727.5 grams, and thosein the tailing 239 grams. The reagent was used in the proportion ofabout 32 pounds per ton of clay.

In yet another test wherein 1000 grams of the crude clay were pulped inabout three liters of water, the sulfite waste liquor was added in theproportion of about 30.8 pounds per ton of clay, i. e., about 12 cc. ofthe liquor being used in the test. The pulp and reagent were treated inthe Callow cell for twenty minutes and the resulting froth concentratewas then re-floated, in the Callow cell, twice. The rougher concentrate,i. e., that resulting from the first flotation, weighed 3.6 kilogramswet,--i. e., contained about 16% solids. The final concentrate from thetwo cleanings was a very hlgh quality kaolin, lacking any appreciablecontent of contaminating impurities; indeed the No. 2 middling, while ofsomewhat lower quality, revealed a. substantial absence of impurities.The solids recovery is indicated by the following table:

Although the foregoing tests were all. made with clay fresh from themine, the procedure is.

effective for treatment of other clay compositions, for example, forrecovery of clay in tailing resulting from sedimentation, centrifugingor other fractionating operation on clay. It will also now be understoodthatwthe procedure is susceptible of considerable variation as tothesolids content of t e clay pulp used, the nature of the frothflotation apparatus, the number of cells utilized, the amount of airemployed for frothing, the quantity of the reagent, and other factors,all as may be readily determined by simple tests in the light of theforegoing description and examples, and depending on the nature ofthegiven clay under treatment and the specific results. desired from theflotation. For instance, it has been found in tests of the characterdescribed above, that the sulflte waste liquor (having the statedspecific gravity of about 1.28) may be included in the clay slip forvery efficient froth flotation results, in amounts ranging from about 15to' about 35 pounds per' ton of clay; it being noted that the toughnessof the froth and consequently its clay-elevating power, tend to increasesomewhat with the amount of the reagent, and yet without undesirableefiect of carrying over impurities even at proportions of 30-35 poundsof liquor per ton. I

The exact action of the suliite waste liquor is not fully understood,except that it not only has advantageous frothing characteristics butalso has a peculiar selectivity for clay, as explained above. It is mybelief that the clay-selecting action stems at least partly from thelignin material in the waste liquor, which is reported to be present ina sulfonic form, say a lignosulfonate. Although the exact chemicalconstitution of sulflte waste liquor is not known, it appears that othercomponents have some bearing, including the presence of fat or fattymaterial, probably in the form of fatty acid soap, which contributes tothe frothing characteristics in the clay pulp undergoing treatment. Onthe other hand, soaps alone, although efficient frothing agents, do notappear to produce worth while results in treatment of clay by frothflotation, especially for separation of impurities of the type describedabove.

It is to be understood that other sulfltewaste liquors, or concentratesor extracts thereof, may be used in many cases. Examples of otherproducts generally classifiable as sulflte waste liquor are thematerials commercially available under the trade names, respectively, ofSuper- Spruce and Spruce Extract," which are solid products understoodto be derived by evaporating down the actual waste liquor from sulfitepulp mills.

It will be understood that the-invention is not limited to the specificprocedures hereinabove described, but may be carried out in other wayswithout departure from itsspirit, asdefined by the following claims.

I claim: 7

1. In the treatment of clay material, the steps comprising establishinga clay pulp containing sulfite waste liquor and blowing air into thepulp to produce a clay-selecting froth.

2. A method of purifying clay, comprising establishing a clay pulpcontaining sulflte waste liquor, aerating the pulp to produce a rising,clay-lifting, froth column selectively favoring the elevation of clayparticles therein rather than contaminating particles, andcollecting thefroth for recovery of purified clay.

3. A method of treating clay material, comprising establishing a claypulp and subjecting the pulp to froth flotation treatment in thepresence of sulflte waste liquor for promoting the elevation of clay infroth.

4. A'method of treating clay material, comprising establishing a claypulp, and subjecting the pulp to froth flotation treatment in thepresence of sulflte waste liquor, by directly aerating and agitating thepulp, to produce a clay-bearing froth. I

5.-A method of separating clay from contaminating particles of mica,sand, ilmenite and iron compounds, comprising subjecting the clay tofroth flotation treatment, including direct aeration of a pulp of theclay, in the presence of sulflte waste liquor.

6. A method of separting clay from particlgs

